Coolant mixture separator assembly for use in a polymer electrolyte membrane (PEM) fuel cell power plant

ABSTRACT

A liquid-gas separator assembly is used in separating gas bubbles from a liquid coolant which liquid coolant is used in a polymer electrolyte membrane (PEM) fuel cell power plant. The assembly includes a cylindrical housing containing a central tube which is surrounded by an annular chamber. The annular chamber is defined by the outer surface of the central tube and the inner surface of the cylindrical housing. An inlet line injects a stream of the coolant from the fuel cell stack area of the power plant into the bottom of the central tube in a tangential flow pattern so that the coolant and gas bubble mixture swirls upwardly through the central tube. The swirling flow pattern of the coolant and gas bubble mixture causes the gas bubbles to separate from the liquid coolant so that the gas in the mixture will migrate to the central portion of the swirl tube and the liquid component of the mixture will centrifugally migrate to the inner wall of the swirl tube. The gaseous component of the separated mixture is then expelled from the housing through an outlet in the upper portion of the housing, and the coolant liquid descends through the annular chamber to the bottom of the housing where the coolant liquid will be returned to the cell stack area of the power plant. The gas bubbles may include reactant from either the cathode or the anode. The separator of this invention is particularly useful in mobile applications since it is less sensitive to vehicular acceration forces.

TECHNICAL FIELD

The present invention relates to a separator assembly for separating gasbubbles from the liquid constituent of a coolant fluid which has beenused to cool a PEM fuel cell power plant cell stack. The coolant fluidis drawn from the power plant cell stack and is pumped to the separator.Gas bubbles that have become entrained in the coolant fluid duringcooling of the cell stack are removed from the coolant liquid in theseparator. The gas bubble-free coolant liquid is then returned to thepower plant system and subsequently to the cell stack.

BACKGROUND OF THE INVENTION

The temperature of the fuel cell stack portion of a PEM fuel cell powerplant is regulated by a coolant stream which absorbs heat from the cellsin the stack. In PEM type fuel cell power plants that utilize porousplate water transfer elements which are directly exposed to the liquidcoolant, the coolant will also will entrain gas bubbles which arederived from the porous water transfer plates as the coolant streampasses through the cell stack area of the power plant. U.S. Pat. No.5,503,944 dated Apr. 2, 1996, which is incorporated herein in itsentirety, discloses a PEM fuel cell power plant which includes porouswater transfer plates which absorb water that is formed on the cathodeside of the electrolyte membranes in the fuel cells. The absorbed waterpasses through the porous plates and enters the circulating coolantstream which is used to control the temperature of the cells. Thecathode water also includes air bubbles that are passed through theporous plates and thus enter the coolant stream. A similar phenomenon onthe anode side causes gaseous fuel constituents to pass through itsporous water transfer plate. Since the coolant stream is constantlyrecycled through the fuel cell stack, the amount of gas entrained in thecoolant stream will increase with time. The resultant build up of gasbubbles which are entrained in the coolant stream will adversely affectthe cooling capacity of the coolant stream. Entrained gas bubbles alsoadversely affect the ability of the coolant pump to recirculate thecoolant liquid by forming a two phase mixture in the coolant liquidthereby rendering the coolant liquid difficult to pump. Therefore, thegas bubbles should be removed from the coolant stream during therecycling of the coolant stream in the power plant in order to maintainthe ability of the coolant stream to regulate the operating temperatureof the power plant. Separating the gas bubbles from the coolant liquidwill also allow the use of simpler, lower cost, longer life coolantrecirculation pumps with a net positive suction head, such as acentrifugal type pump.

DISCLOSURE OF THE INVENTION

This invention relates to a system and method for removing gas bubbleswhich are entrained in a recirculated coolant stream in a PEM fuel cellpower plant, which power plant employs porous anode and cathode watertransfer plates, the cathode transfer plate being operative to transferproduct water from the cathode to the coolant stream in the power plant.The system and method of this invention involve the use of a vortexseparator mechanism which serves to separate entrained gas bubbles froma recirculating liquid coolant stream. The coolant stream, after itexits the fuel cell area of the power plant, is drawn into theseparator. The gas bubble-coolant liquid mixture enters the bottom ofthe separator and is vortexed upwardly through a central portion of theseparator where the liquid coolant in the mixture is flung radiallyoutwardly in the separator by centrifugal force, and the entrained gasbubbles remain in a central funnel in the vortex. The separated funneledgas bubble stream is drawn out of the separator through a central upperoutlet. The liquid coolant is gravimetrically removed from the separatorthrough an outer annular passage in the separator. The liquid coolant isthen pumped out of the separator and returned to the fuel cell stackportion of the power plant.

The separator of this invention is structured as follows. The separatorincludes a cylindrical housing having a lower end and an upper end. Thelower end of the separator includes a manifold which receives thecoolant liquid-gas bubble mixture from the fuel cell stack area of thepower plant. The housing includes an inner tubular part whichcommunicates with the manifold, and an outer annular part whichcommunicates with the upper end of the inner tubular part of theseparator. An inlet tube opens into the manifold in a tangentialfashion. The inlet tube introduces the liquid coolant and gas bubblemixture into the manifold in a swirling flow stream which creates avortex flow pattern in the manifold. The swirling mixture flows upwardlyinto the inner tubular part of the separator. The mixture separates intoa radially outward liquid component and a central gas component. Theouter liquid component flows upwardly along the wall of the innertubular part until it reaches the top of the inner tubular partwhereupon it cascades over the top of the inner tubular part anddescends through the outer annular part of the separator to the bottomof the separator where it is pumped out of the separator by an upstreampump. The liquid coolant is then pumped through a heat exchanger whereits temperature is lowered to a temperature suitable for cooling thefuel cell stack in the power plant, to which it is returned. The centralgas stream in the tubular part of the separator is vented from theseparator housing through a top wall of the housing. The liquid coolantis recirculated through the separator after each cooling pass throughthe fuel cell stack.

It is therefore an object of this invention to provide a PEM fuel cellpower plant assembly which includes porous water transfer plates thatwick water away from the cathode side of the cells in the power plant.

It is an additional object of this invention to provide an assembly ofthe character described wherein the cathode water is wicked through theporous plates into a coolant stream which controls the temperature ofthe fuel cells in the power plant.

It is a further object of this invention to provide an assembly of thecharacter described which includes a separator that separates entrainedgas bubbles from the liquid coolant stream after the coolant streamleaves the fuel cell area of the power plant.

It is another object of this invention to provide an assembly of thecharacter described wherein the separator creates an upwardly directedswirling vortex flow pattern in the coolant-gas mixture thatcentrifugally separates the liquid coolant from the gas in the mixture.

These and other objects of the invention will become more readilyapparent from the following detailed description thereof when taken inconjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a fuel cell power plant which includes aseparator that is formed in accordance with this invention;

FIG. 2 is a sectional view of the separator assembly formed inaccordance with this invention;

FIG. 3 is a cross sectional view of the separator assembly taken alongline 3—3 of FIG. 2; and

FIG. 4 is a cross sectional view of the separator assembly taken alongline 4—4 of FIG. 2.

SPECIFIC MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings FIG. 1 is a schematic view of a PEM fuelcell power plant system which is designated generally by the numeral 2,and which incorporates the gas-liquid separator assembly 4 of thisinvention. The power plant system 2 includes a PEM cell stack 6 having acathode side 8 and an anode side 10 which are disposed on opposite sidesof the electrolyte membrane 9. An operating temperature-controllingcooler 12 is disposed on the cathode side 8 and on the anode side of anadjacent cell of the stack 6 gas is fed into the cathode side 8 via line14 and fuel is fed into the anode side 10 via line 16. The fuel can bereformed natural gas, or some other hydrogen-containing gas. A liquidcoolant is fed into the cooler 12 via a line 18 from a coolantaccumulator 20. As noted above, water which forms on the cathode side 8of the electrolyte 9 is transported into the cooler 12 along with gasbubbles through a porous plate 22, and fuel gas is likewise transportedto the coolant stream from the anode side of an adjacent cell. Thecoolant exits from the cooler 12 through a line 24 which leads to theseparator assembly 4. The entrained gas bubbles are separated from theliquid coolant in the separator assembly 4 in a manner which will bedescribed in greater detail hereinafter, and the separated gas componentis withdrawn from the separator assembly 4 through a line 26 which isconnected with the accumulator 20. A vacuum pump 25 is operative to drawthe gas out of the separator assembly 4. Gas separated from the coolantstream is then vented from the accumulator 20 through line 21. Thegas-free liquid coolant exits the separator assembly through a line 28.A pump 30 moves the coolant through the line 28 and into a line 32 whichleads to a heat exchanger 34 where the temperature of the coolant islowered to an appropriate temperature for cooling the stack 6. Thecoolant is transferred from the heat exchanger 34 through a line 36 backto the accumulator 20 so that it can be reused to cool the stack 6.

Referring now to FIGS. 2–4, details of the separator assembly 4 areshown. The separator assembly 4 includes a cylindrical housing 38 whichis mounted on an cylindrical manifold base 40. The line 24 enters themanifold base 40 tangentially as is shown in FIG. 4. The coolant-gasmixture thus forms a swirling flow pattern in the manifold base 40 asindicated by the arrow A as shown in FIGS. 2 and 4. The assembly 4 alsoincludes an inner tubular member 42 which is inwardly spaced from theside wall of the housing 38 so as to form an annular space 44 betweenthe outer surface of the member 42 and the inner surface of the housing38. The bottom of the tube 42 opens into the interior of the manifold 40and the swirling coolant liquid-gas mixture is impelled upwardly throughthe tube 42 and swirls upwardly through the tube 42 as indicated by thearrows B. As the mixture swirls upwardly through the tube 42, the liquidconstituent will centrifugally separate from the gas constituent so thatthe liquid constituent swirls upwardly on the inner surface of the tube42, and the gas constituent swirls upwardly in the central portion ofthe tube 42. The separated gas constituent is ejected from the housing38 through a central opening 46 which is connected to the line 26 shownin FIG. 1.

The separated liquid coolant constituent spills over the upper edge ofthe tube 42 and flows downwardly through the annular space 44, asindicated by the arrows C. The liquid coolant constituent is then pumpedout of the annular space 44 through the line 28. As seen in FIG. 3, theannular space 44 can be provided with radial fins 48 which will convertthe liquid swirling flow to a linear flow. Thus the coolant liquid willquiescently pool in the lower portion of the annular space 44 prior tobeing withdrawn from the separator 4 through the line 28.

It will be readily appreciated that the separator of this assembly canefficiently separate a gas-liquid mixture into separate componentsthereby removing the gas from the liquid. The separator is particularlyuseful in removing entrained gas bubbles from a liquid coolant stream ina PEM fuel cell power plant assembly. By removing the entrained waterbubbles from the liquid coolant, the cooling capacity of the coolant isimproved, and the coolant can be recirculated back to the cell area ofthe power plant and reused to control the temperature of the cells inthe power plant. Removal of the gas bubbles also enables the use ofsimpler, lower cost, long life recirculating pumps with improved suctionheads. The hydraulic water head available to the coolant pump ismaximized by the up-flow vortex pattern, thus reducing the pump's netpositive suction head requirement. Use of the up-flow vortex flowpattern also enables the separator to be quite compact, essentially thesame size as a coffee can, which is about six inches high and about fiveinches in diameter. These dimensions are approximate and are notintended to limit the invention as claimed.

Since many changes and variations of the disclosed embodiment of theinvention may be made without departing from the inventive concept, itis not intended to limit the invention otherwise than as required by theappended claims.

1. An assembly for separating a liquid component from a gas component ina liquid-gas mixture, said assembly comprising: a) an vertically axiallyelongated housing which is mounted on a manifold base, a first passageopening into said manifold base for introducing the liquid-gas mixtureinto said manifold base in a manner which creates an upwardly swirlingstream of the liquid-gas mixture in the manifold base; b) a tubularmember mounted in said housing, said tubular member opening into saidmanifold base so as to receive the upwardly swirling stream of theliquid-gas mixture from the manifold base; c) an annular spaceinterposed between said tubular member and an inner wall of saidhousing, said annular space being operative to receive a separatedliquid component of the mixture from said tubular member, and saidannular space being provided with radial fins which null swirling flowpatterns in the liquid component as the latter descends through saidannular space and said annular space being operative to gravimetricallychannel said separated liquid component downwardly therethrough; and d)a vent in said housing, said vent being operative to remove gas from thehousing, which gas has been separated from the liquid-gas mixture in thehousing.
 2. The assembly of claim 1 further comprising an outlet in alower end of said annular space, which outlet is operative to remove theseparated liquid component from said housing.